Studies on two classes of positive electrode materials for lithium-ion batteries

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The development of advanced lithium-ion batteries is key to the success of many technologies, and in particular, hybrid electric vehicles. In addition to finding materials with higher energy and power densities, improvements in other factors such as cost, toxicity, lifetime, and safety are also required. Lithium transition metal oxide and LiFePO<sub>4</sub>/C composite materials offer several distinct advantages in achieving many of these goals and are the focus of this report. Two series of layered lithium transition metal oxides, namely LiNi<sub>1/3</sub>Co<sub>1/3-y</sub>M<sub>y</sub>Mn<sub>1/3</sub>O<sub>2</sub> (M=Al, Co, Fe, Ti) and LiNi<sub>0.4</sub>Co<sub>0.2-y</sub>M<sub>y</sub>Mn<sub>0.4</sub>O<sub>2</sub> (M = Al, Co, Fe), have been synthesized. The effect of substitution on the ... continued below

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179 p.

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Wilcox, James Douglas December 1, 2008.

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The development of advanced lithium-ion batteries is key to the success of many technologies, and in particular, hybrid electric vehicles. In addition to finding materials with higher energy and power densities, improvements in other factors such as cost, toxicity, lifetime, and safety are also required. Lithium transition metal oxide and LiFePO<sub>4</sub>/C composite materials offer several distinct advantages in achieving many of these goals and are the focus of this report. Two series of layered lithium transition metal oxides, namely LiNi<sub>1/3</sub>Co<sub>1/3-y</sub>M<sub>y</sub>Mn<sub>1/3</sub>O<sub>2</sub> (M=Al, Co, Fe, Ti) and LiNi<sub>0.4</sub>Co<sub>0.2-y</sub>M<sub>y</sub>Mn<sub>0.4</sub>O<sub>2</sub> (M = Al, Co, Fe), have been synthesized. The effect of substitution on the crystal structure is related to shifts in transport properties and ultimately to the electrochemical performance. Partial aluminum substitution creates a high-rate positive electrode material capable of delivering twice the discharge capacity of unsubstituted materials. Iron substituted materials suffer from limited electrochemical performance and poor cycling stability due to the degradation of the layered structure. Titanium substitution creates a very high rate positive electrode material due to a decrease in the anti-site defect concentration. LiFePO<sub>4</sub> is a very promising electrode material but suffers from poor electronic and ionic conductivity. To overcome this, two new techniques have been developed to synthesize high performance LiFePO<sub>4</sub>/C composite materials. The use of graphitization catalysts in conjunction with pyromellitic acid leads to a highly graphitic carbon coating on the surface of LiFePO<sub>4</sub> particles. Under the proper conditions, the room temperature electronic conductivity can be improved by nearly five orders of magnitude over untreated materials. Using Raman spectroscopy, the improvement in conductivity and rate performance of such materials has been related to the underlying structure of the carbon films. The combustion synthesis of LiFePO<sub>4</sub> materials allows for the formation of nanoscale active material particles with high-quality carbon coatings in a quick and inexpensive fashion. The carbon coating is formed during the initial combustion process at temperatures that exceed the thermal stability limit of LiFePO<sub>4</sub>. The olivine structure is then formed after a brief calcination at lower temperatures in a controlled environment. The carbon coating produced in this manner has an improved graphitic character and results in superior electrochemical performance. The potential co-synthesis of conductive carbon entities, such as carbon nanotubes and fibers, is also briefly discussed.

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179 p.

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  • Related Information: Designation of Academic Dissertation: Doctor of Philosophy; Academic Degree: PhD.; Name of Academic Institution: University of California, Berkeley; Location of Academic Institution: Berkeley, CA

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  • Report No.: LBNL--3186E
  • Grant Number: AC02-05CH11231
  • Grant Number: W-7405-ENG-36
  • DOI: 10.2172/983034 | External Link
  • Office of Scientific & Technical Information Report Number: 983034
  • Archival Resource Key: ark:/67531/metadc1013002

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • December 1, 2008

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  • Oct. 14, 2017, 8:36 a.m.

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Wilcox, James Douglas. Studies on two classes of positive electrode materials for lithium-ion batteries, thesis or dissertation, December 1, 2008; United States. (digital.library.unt.edu/ark:/67531/metadc1013002/: accessed September 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.